Many applications require incremental positioning of movable machine elements. Among these are magnetic transducers on magnetic disc and drum drives; optical transducers on optical disc drives; platens and pen carriages on incremental plotters; magentic transducers on multi-track, moving head, magnetic tape drives; platens, platen carriages, print head carriages, print wheels, print thimbles, print balls, and print drums on computer output printers, word processors, teletypes, and typewriters; wafer steppers; and numerically controlled machine tools.
Ideal positioning of these machine elements requires minimal overshoot, minimal oscillation, and minimal dead band. If the power input to the positioning apparatus is of an analog nature, then the apparatus should convert that input into a specific incremental output. If the power input is of an incremental nature, then the positioning apparatus should refine that incremental input into precise positional increments.